1. Field of the Invention
The present invention relates to a discharge head for an electrostatic recording device used in machines such as printers, and facsimiles. In particular, the invention relates to a discharge head that generates charged particles (ions) and records images by means of the ions generated.
2. Description of the Related Art
There are various charge generating devices for use in electrostatic recording apparatuses. One such device is disclosed in U.S. Pat. No. 4,155,093 (Japanese Patent Laid Open No. 54-53537). As shown in FIG. 14, this device consists of a first set of electrodes 41 that are disposed on one side of a planar dielectric body 40. Numerous holes 42 for generating ions are formed on the first set of electrodes 41, as shown in FIG. 15, to form air gap regions 43 between the end face of the first set of electrodes 41 and the surface of the dielectric body 40. A second set of electrodes 44 are provided on the surface of the dielectric body 40 opposite the first set of electrodes 41. The surface of the dielectric body 40 on which the first set of electrodes 41 are disposed is arranged to face a recording body such as dielectric paper 45. Applying an AC voltage between the first set of electrodes 41 and the second set of electrodes 44 causes ions to be generated by a creeping discharge that is produced in the air gap region 43 along the surface of the dielectric body 40. The device is designed to record an image by electrostatically charging the surface of the dielectric paper 45 by generating ions and emitting them in a direction perpendicular to the creeping discharge (perpendicular to the surface of the dielectric body 40).
The prior art device has the following problems. First, since ions for electrostatically charging the dielectric paper 45 are emitted in a direction that is both perpendicular to the creeping discharge and perpendicular to the surface of the dielectric body 40, ion generation efficiency is lower than it would be if ions were emitted only in the direction of generation of the creeping discharge. Since it takes added time to generate the ions needed to charge the surface of the dielectric paper 45 to a predetermined potential, recording speed is substantially limited.
In addition, it is necessary to apply a high AC voltage to the first set of electrodes 41 and the second set of electrodes 44 in order to obtain the requisite ion charging. This increases creeping discharge and leads to electrical, chemical and thermal deterioration of the electrodes 41 and 44, and the dielectric body 40. In addition, ion generation becomes difficult due to an increase in compounds generated by the discharge that attach to the first set of electrodes 41 and prevent the device from being stably used for an extended period of time.
Moreover, since image recording is carried out by disposing the the first set of electrodes 41 on one side of the dielectric body 40 to contact a recording body 47, the area of the recording part has to be increased. For this reason, in a device that makes use of a drum-like recording body, the area of the recording part is increased so that the ratio of the area of the recording part to the area of the surrounding recording body drum 47 becomes large, as shown in FIG. 16. This results in a large sized recording device.
The applicants of the present invention have already proposed (Japanese Patent Application No. 62-212958), a device intended to solve the above-mentioned problems. This previous electrostatic recording device (not prior art) was designed to (1) carry out recording at high speed by generating ions efficiently, (2) prolong the life of the recording device by lowering the voltage necessary for generating the creeping discharge and thereby prevent deterioration of the electrodes and the dielectric members, and (3) miniaturize and make compact the recording head.
As shown in FIG. 17 and FIG. 18, the above-mentioned device has a discharge head 53 wherein a first set of electrodes 50 each have a linear form and are embedded in a solid dielectric substrate 51. The first set of electrodes 50, are disposed at predetermined intervals from each other and have their tips exposed. A second electrode 52 is embedded on the reverse side of the dielectric substrate to perpendicularly intersect the tips of the first set of electrodes 50, and form a spatial region G for generating a creeping corona discharge between the tips of the first set of electrodes 50 and the solid dielectric substrate 51. Recording of electrostatic images is accomplished by arranging the disk head 53 so that the tips of the first set of electrodes 50 face a recording body (not shown), and applying an AC voltage between the first set of electrodes 50 and the second electrode 52 to generate a creeping corono discharge R that extends from the tips of the first set of electrodes 50 to the second electrode 52 via the surface of the solid dielectric substrate 51. However, this proposed device has the following drawbacks. The first set of electrodes 50 extend linearly toward the recording body, whereas the second electrode 52 is disposed so as to perpendicularly intersect the first electrodes at their tips. Due to this arrangement, a voltage applied between the first and second electrodes 50 and 52, causes the resulting creeping corona discharge R to spread as shown in FIG. 19. This results in a spreading of the image recorded by the first set of electrodes 50 and a lowering of the resolution of the image. In addition, cross-talk occurs due to adjacent electrodes 50 simultaneously discharging ions.